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Phosphazene bases are extremely strong and uncharged bases, built on a unit where a nitrogen basic center is double bonded to pentavalent phosphorus.[1,2] Through oligomerization of the peralkylated triaminoiminophosphorane unit, the basicity improves dramatically (Figure 1). In the case of the monomeric phosphazene base, its basicity is about a 2-3 units beyond the basicity range of DBU (MeCNpKBH+ 24.3) and DBN, but reaches a MeCNpKBH+ of over 40 in the case of a tetrameric P4 phosphazene base (DBU = 1,8-Diazabicyclo[5.4.0]undec-7-ene, DBN = 1,5-Diazabicyclo- [4.3.0]non-5-ene).

We offer these reagents as monomeric (P1 and BEMP), dimeric (P2), and tetrameric (P4) bases, with different side chains to control their sterical hindrance. Scheme 1 shows the basicity of phosphazene bases compared to other bases (in the absolute acetonitrile scale), as well as compared to the acidity of important organic compounds or classes of compounds.

Properties of Phosphazene Bases:

High solubility in apolar to moderately polar solvents (e.g. hexane, toluene or THF)